letter’s envelope vs envelope of the letter , which one is correct , example

RULE - Living beings (सजीवों )का possessive ('s) तथा (of ) दोनों से बनाई जाती हैं जबकि non living beings का possessive सिर्फ (of ) से बनाई जाती है |

Example : 
where is the letter’s envelope? / no error

Correct Sent-  where is the envelope of the letter.

Reason - Letter , non living thing है इसलिए of आएगा|

Download Yvid : Create Amazing video from your images : for you Gilrfriend , Birthday , Marriage ,GoodMorning Message

https://play.google.com/store/apps/details?id=com.torus.yvideo